Production of titanium dioxide



United States Patent O PRODUCTION OF TITANIUM DIOXIDE Eugene Wainer, Cleveland Heights, Ohio, assignor to Horizons Incorporated, Cleveland, Ohio, a corporation of New Jersey No Drawing. Filed Mar. 14, 195$,Ser. No. 721,338

4 Claims. (Cl. 23-202) This invention relates to a process for beneficiating titaniferous minerals containing various impurities to produce a rutile product sufliciently free of heavy metal impurities to be useful as heavy grade rutile in the porcelain enamel industry and in other applications.

Titanium occurs in nature in the form of-oxides usually associated with iron and/or alkaline earth metals. Ilmenite, one of the more common naturally occurring titanium ores usually contains iron in an amount corresponding approximately to the formula FeO-TiO In addition to the iron, ilmenite ores usually have substantial quantites of silica or silicate minerals and pyrites or other sulphur compounds associated with the ore and compounds of various other heavy mineral elements such as chromium, molybdenum, tungsten, etc. in amounts which are sufficient to disqualify the ores from many commercial uses. By the practice of my invention the titanium dioxide content of the ore is recovered freed from the siliceous and sulphur-containing gangue and also from compounds of the heavy mineral elements, particularly chromium, and is then sufficiently pure for use in the manufacture of porcelain enamels.

In a co-pending application, Serial No. 590,101, I have described a procedure whereby ilmenite ores may be beneficiated to obtain a product substantially free of the silica and pyrites existing in the ilmenite. In this present invention I have now found the means for further beneficiating to remove not only siliceous and sulphur-containing gangue but also to remove compounds of the metal chromium.

Chromium compounds in very small amounts produce distinct colorations in titanium dioxide. For example, chromium nitrate generally imparts a light-gray-tan color, chromium alum imparts a buff color, and potassium dichromate imparts a dark buff color to titanium dioxide pigments. The presence of even minute amounts of chromium, that is amounts corresponding to more than 0.0015 Cr O deleteriously affects the light reflectance properties of titanium dioxide porcelain enamels.

I have now found that when crushed ilmenite ore is appropriately treated prior to digestion in aqueous hydrochloric acid solution, the amount of any chromium impurity remaining in the recovered product may be diminished to a level below that which imparts a color to the rutile product.

In accordance with my invention, the ilmenite ore, after crushing, is subjected to a solid-solid reaction effected at temperatures up to and including 1000 C. Preferably at least one alkali or alkaline earth carbonate admixed with a carbonaceous reducing agent is heated in intimate contact with the finely divided ilmenite ore to produce a sinter in which the chromium is present in the form of one or more chromates. The temperature of the reaction is such that the corresponding alkali or alkaline earth titanate is formed but only a portion, approximately 25%, of the iron content of the ore is reduced to the metallic state. In order to assure that the chromium content of the ore is fully oxidized to the chromate 2,941,863 Patented June 21, 1960 2 state and that excess carbon, petroleum coke or other reducing agent is removed, the sinter is broken up and roasted for about one hour at 600C.700C. The resulting product is then found to be particularly susceptible to a treatment whereby the chromium compounds may be removed from the titanium compounds present.

In the practice of my invention the titaniferous ore is first crushed, then intimately blended with at least 'one alkali or alkaline earth carbonate and with an added reducing agent such as carbon, and the resulting mixture of ore, carbonate and reducing agent is sintered in a neutral or reducing atmosphere at temperatures up to 1000 C. and preferably between 500 C. and 1000 C. fora period of several hours. In the 'sintering process, the titanium values present are converted to titanates and the chromium values are converted to chromate. border to remove excess carbon in those instances in which it is objectionable, the sinter is broken into pieces and the broken up sinter may be processed to remove unused reducing agent, e.g. by screening, before it is roasted '-at about 600 C. to burn off the excess carbon. The roasted product is then broken up and leached in water or in a dilute water solution containing-a small percentage'of alkali peroxide to remove the solubilized chromium impurity in the ore. The solid product remaining after leaching is then digested in hydrochloric acid at temperatures slightly below the boiling point for between 1 and 2 days. The iron compounds are thereby dissolved as chlorides and the alkali titanates are reacted to produce hydrated titanium dioxide. After digestion the solids present are separated into a fraction coarser than 325 mesh (Tyler standard) and a fraction finer than 325 mesh. The coarser fraction which has been found to contain virtually all of the silica and sulfur compounds is discarded. The finer fraction is washed free of soluble iron compounds and calcined'to produce a heavy grade rutile suitable for the manufacture of enamel.

The following examples will serve further to illustrate the novel aspects of my invention but are intended to be illustrative rather than limitative of my process.

Example 1 One hundred grams of minus 325 mesh ilmenite containing about 0.05% chromium were intimately mixed with 40 grams of CaCO and 8 grams of carbon black, placed in a covered carbon crucible and reacted for 15 hours at 900 C. The resulting sinter was broken up and leached in water at 90 C. for 4 hours. The leach liquor tested positively for chromium. The leached sinter was separated from excess carbon by decantation and was then dewatered on a Biichner funnel. The dewatered cake was then dried and digested in concentrated HCl solution at about C. for about 1 day. The digestion product resulting from this treatment was filtered and wet screened to separate the fine solid hydrated rutile from the iron chlorides in the digestion liquid and from the coarser solid silica and sulfur impurities. The hydrated rutile recovered was washed with dilute HCl solution, and calcined for one hour at 800 C. The rutile product obtained was found to contain less than 0.0015% chromium (expressed as Cr O and was therefore suitable as raw material in an enamel formulation.

Example 11 The procedure of Example I was repeated with another sample of the same ore, but before leaching the crushed sinter was roasted in an oxidizing atmosphere to burn out any free carbon present. The roasted product was then digested in HCl as in Example I. The rutile product obtained after digestion and separation of the undesired liquid and solid contaminants was formulated into an enamel frit with satisfactory light reflectance.

Example III Another sample of ore was treated in the same manner as described in Example II, except that liquid used to leach the sinter after roasting was a 1% aqueous soluion of N3202- contained 0.001% Cr (expressed as Cr O Example IV 1 The procedure of Example II was repeated using 40 grams of Na cO in place of the 40 grams of CaCO The product was not materially difierent from that obtained in Example II.

L While a 1% aqueous solution of Na O has been disclosed in Example III, I have found that dilute solutions containing up to 10% Na o are effective in dissolving out-the chromates, although for reasons of economy I prefer strengths of between 0.5% Na O and 2% Na O Iclaim: I

p 1. A process for recovering heavy grade rutile from starting materials containing titanium dioxide associated with impurities including compounds of iron and compounds of chromium which comprises; crushing the starting materials to a finely divided solid powder; forming a mixture of the crushed starting material, a cabonaceous reducing agent and at least one carbonate from the group consisting of alkali metal carbonates and alkaline earth The rutile product ultimately recovered metal carbonates; heating the mixture to between 500 C. and 1000 C. for a time sufiicient to reduce a portion of the iron compounds to metallic iron; crushing the resulting product; roasting the crushed product at about 600 C-. to remove unspent reducing agent and to insure oxidation of the chromium; leaching the roasted material with a dilute aqueous solution of an alkali metal peroxide to dissolve the chromates present; thereafter separating the iron compounds from the titanium values present by HCl digestion; and recovering the hydrated titanium oxide digestion product.

2. The process of claim 1 in which the recovered hydrated oxideis thereafter calcined to produce'a fired rutile.

3. The process of claim l inwhich a 1% solution of Na O constitutes the dilute aqueous solution of alkali metal peroxide.

4. The process of claim 1 inlwhich unused reducing agent is screened out of .the crushed material prior to roasting.

References Cited in the file of this patent UNITED STATES PATENTS 1,206,798 Barton Dec. 5, 1916 1,734,034 Gregory Nov. 5,1929 1,845,633 Specht Feb. 16, 1932 2,496,993 Goda Feb. 7, 1950 2,530,616 Kingsbury et al Nov. 21, 1950 

1. A PROCESS FOR RECOVERING HEAVY GRADE RUTILE FROM STARTING MATERIALS CONTAINING TITANIUM DIOXIDE ASSOCIATED WITH IMPURITIES INCLUDING COMPOUNDS OF IRON AND COMPOUNDS OF CHROMIUM WHICH COMPRISES, CRUSHING THE STARTING MATERIALS TO A FINELY DIVIDED SOLID POWDER, FORMING A MIXTURE OF THE CRUSHED STARTING MATERIAL, A CABONACEOUS REDUCING AGENT AND AT LEAST ONE CARBONATE FROM THE GROUP CONSISTING OF ALKALI METAL CARBONATES AND ALKALINE EARTH METAL CARBONATES, HEATING THE MIXTURE BETWEEN 500* C. AND 1000* C. FOR A TIME SUFFICIENT TO REDUCE A PORTION OF THE IRON COMPOUNDS TO METALLIC IRON, CRUSHING THE RESULTING PRODUCT, ROASTING THE CRUSHED PRODUCT AT ABOUT 600* C. TO REMOVE UNSPENT REDUCING AGENT AND TO INSURE OXIDATION OF THE CHROMIUM, LEACHING THE ROASTING MATERIAL WITH A DILUTE AQUEOUS SOLUTION OF AN ALKALI METAL PEROXIDE TO DISSOLVE THE CHROMATES PRESENT, THEREAFTER SEPARATING THE IRON COMPOUNDS FROM THE TITANIUM VALUES PRESENT BY HC1 DIGESTION, AND RECOVERING THE HYDRATED TITANIUM OXIDE DIGESTION PRODUCT. 